How is the protest unfolding?

The walkouts began at 10:00 in the eastern US (14:00 GMT) and moved west across America’s time zones.

Organisers of the National School Walkout, who were also behind the Women’s March in January 2017 against Mr Trump’s inauguration, called on “students, teachers, school administrators, parents and allies” to take part.

On their website, they accuse Congress of “inaction to do more than tweet thoughts and prayers in response to the gun violence plaguing” schools and neighbourhoods.

Schools taking part included Colorado’s Columbine High School where 13 people were shot dead by two students in 1999.

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“I should be writing my college essay, not my will” a student’s sign in New York says

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Students in the Washington DC area marched to Congress and the White House

Image copyrightReuters

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Students at Marjory Stoneman Douglas High School walked to the football field

In Parkland, families and supporters applauded as thousands of students slowly marched on to the Stoneman Douglas school football field.

School principal Ty Thompson called on them to stage the “biggest group hug”.

A large crowd of students from the Washington DC area gathered outside the White House holding signs reading “Protect People Not Guns” and chanting “Never again” and “Enough is enough”.

Some students also gathered at Capitol Hill where they were addressed by the Senate and House Democratic leaders, Chuck Schumer and Nancy Pelosi.

“We’re all moved by your eloquence and your fearless insistence on action to prevent gun violence,” Ms Pelosi told them.

“Thank you for bringing your urgency to this fight, to the doorstep of America, the doorstep of the Capitol of the United States.”

Image copyrightTeagan Huenke

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Students in suburban Chicago honoured members of their own community who have been killed with guns

Students in Cherry Hill, New Jersey, stood in a heart formation to pay tribute to the Parkland victims.

In New York, hundreds of students from Fiorello H LaGuardia High School – many dressed in orange, the colour of the gun-control movement – took to the streets of Manhattan.

“Thoughts and prayers are not enough,” read one sign.

New York Governor Andrew Cuomo also joined protesters for a symbolic “die-in” – lying down in a street in Lower Manhattan.

How have the authorities responded?

The US House of Representatives on Wednesday voted 407-10 in support of a bill to authorise $50m (£36m) in federal grants for training, anonymous reporting systems, threat assessments, intervention teams and school and police coordination. It does not address gun control.

It is unclear when the Senate, which is expected to take up a separate measure to strengthen background checks for gun buyers, will consider the bill.

Image copyrightEPA

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US House Minority Leader Nancy Pelosi addressed students outside the US Capitol

The House measure would not allow the approved funding to be used to arm teachers or school personnel, a provision the White House has backed.

President Trump tweeted his support of the bill on Wednesday afternoon.

Today the House took major steps toward securing our schools by passing the STOP School Violence Act. We must put the safety of America’s children FIRST by improving training and by giving schools and law enforcement better tools. A tragedy like Parkland can’t happen ever again!

Chuck Schumer, leader of the opposition Democrats in the Senate, dismissed the White House’s action plan as “baby steps”.

When the state of Florida passed a gun control law which raises the legal age for buying rifles to 21, it was sued by America’s main gun lobby, the National Rifle Association, which argues that such curbs violate the US constitution.

Media captionShoes mark young victims of gun violence

In a separate incident on Tuesday, a teacher in California is believed to have accidentally fired a gun in a classroom, injuring a student.

Police said the teacher at Seaside High School, in Monterey County, had been taking a public safety class when he accidentally discharged the weapon into the ceiling.

Officials said one student was injured by either bullet fragments or ceiling debris and was taken to hospital for treatment.

The teacher has been placed on administrative leave and the incident is being investigated, police said.